The present invention relates to a substrate for presensitized plates for use in making lithographic printing plates (herinafter referred to as "PS plate" for simplicity) and more particularly to an aluminum alloy plate used as a substrate for PS plates, which is excellent in processability by electrolytic graining and strength and which is less expensive.
Generally, as substrates for PS plates there have conventionally been used aluminum plates. In such cases, it is necessary to roughen the surface of the aluminum plates in order to improve adhesion thereof to light-sensitive films to be applied and water retention property of non-image areas of the plate.
As such surface roughening treatments, there have been known such mechanical surface graining methods as a ball graining technique, a brush graining technique and a wire graining technique, but recently there have also been adopted an electrolytic surface graining method in which the surface of an aluminum plate is electrochemically roughened using an electrolyte such as those consisting of hydrochloric acid or mainly composed of hydrochloric acid (hereinafter referred to as "hydrochloric acid type electrolytes") or those consisting of nitric acid or mainly composed of nitric acid (hereunder referred to as "nitric acid type electrolytes"). The advance of this electrolytic graining technique has recently been accelerated because it is excellent in plate-making properties and printing properties and it is also favorable for continuous processing of coiled materials.
As substrates for PS plates, there have been employed conventionally, in mechanical surface graining methods, aluminum alloy plates corresponding to A 1100 (purity of aluminum: not less than 99.0% by weight) and A 3003 (purity of aluminum: 98.0 to 98.5% by weight) of JIS standard while, in electrolytic graining methods, those corresponding to A 1050 (purity of aluminum: not less than 99.5% by weight) which provide uniform electrolytically grained surfaces.
However, the foregoing aluminum material A 1050 which is favorable for electrolytic surface graining has low strength because of its high purity of aluminum. Therefore, if its thickness is reduced, the resulting plate is hard to handle and this problem becomes conspicuous in particular when it is subjected to burning in treatment since the plate softens during such treatment. For instance, the printing speed has become high in response to the progress of printing techniques and this leads to increase in stress applied to original printing plates which are mechanically fixed at both ends of the plate cylinder of a printing press. Therefore, the fixed portions of the plate sometimes cause deformation or breakage due to insufficient strength of substrates for lithographic printing plate, which in turn causes troubles such as slippage of images and cutting off of the plate which make the printing operation impracticable. Moreover, it is inevitable to use a relatively thick aluminum alloy plate to ensure mechanical strength such as dimensional stability. This is a primary cause of increase in the cost for manufacturing lithographic printing plates.
As materials for substrate of PS plates disclosed in prior art there have been known aluminum alloys listed below:
__________________________________________________________________________ Sources Alloy Composition (wt %) and Materials Other Disclosed Therein Si Fe Cu Mn Mg Cr Zn Ti Component __________________________________________________________________________ J. P. KOKAI No. 57-89497 (U.S. Pat. No. 4,383,897) 1100 0.375 0.375 0.05 -- -- -- -- -- 3003 0.2 0.15 0.05 0.7 -- -- 0.2 0.2 A19 0.375 0.375 0.05 -- 0.9 -- -- -- J. P. KOKAI No. 54-128453 (U.S. Pat. No. 4,211,619) DIN3.0255 0.3 0.5 0.02 -- -- -- 0.07 0.03 alloy elements max. 0.5 DIN3.0515 0.5 0.5 0.1 0.8.about.1.5 0.about.0.3 -- 0.2 0.2 alloy elements max. 1.5 J. P. KOKAI No. 54-133903 (U.S. Pat. No. 4,301,229) 1S 0.25 -- -- -- -- -- -- -- 2S 0.4 -- -- -- 0.6 -- -- -- 3S -- -- -- 1.2 -- -- -- -- 24S -- -- 4.5 0.6 1.5 -- -- -- 52S -- -- -- -- 2.5 0.25 -- -- 61S 0.6 -- 0.25 -- 1.0 0.25 -- -- 75S -- -- 1.60 -- 2.50 0.30 5.60 -- DE1160639 0.8.about.1.2 0.5 1.4.about.1.6 0.5.about.0.9 0.8.about.1.2 -- 0.1.about.0.3 -- DE1929146 0.2.about.0.4 0.5 0.05.about.0.3 0.8.about.1.4 0.8.about.2.5 -- 0.01.about.0.2 0.01.about.0.05 B = 0.001.about. (U.S. Pat. No. 0.005 3,672,878) (U.S. Pat. No. 3,717,915) DE2537819 0.5.about.1.5 0.05.about.0.5 0.about.0.5 0.005.about.0.4 0.4.about.1.2 0.about.0.3 0.about.0.5 0.about.0.05 B = 0.about.0.005 J. P. KOKAI 0.05.about.0.30 0.15.about.0.30 max. 0.05 -- 0.05.about.0.30 -- -- max. 0.03 B = max. 0.01 No. 58-42745 (U.S. Pat. No. 4,435,230) J. P. KOKAI 0.02.about.0.15 0.1.about.1.0 max. 0.003 max. 0.05 max. 0.05 -- max. 0.05 max. 0.03 No. 58-221254 (E.P. 97318A) J. P. KOKAI max. 0.5 0.05.about.0.8 0.05.about.1 0.3.about.2 max. 1 -- -- max. 0.05 No. 60-63340 J. P. KOKAI max. 0.20 max. 0.50 -- 0.05.about.less -- -- -- max. 0.1 No. 60-230951 than 1.0 (U.S. Pat. No. 4,686,083) J. P. KOKAI max. 0.1 1.2.about.2.1 max. 0.3 0.1.about.0.9 max. 0.1 max. 0.05 max. 0.1 max. 0.1 Fe + Mn = No. 61-35995 1.3.about.2.2 (U.S. Pat. No. 4,672,022) __________________________________________________________________________ "J. P. KOKAI" means "Japanese Patent Unexamined Publication". In this Table, (--) means that there is no disclosure in the correspondin Prior Art.
Among the aluminum alloys listed in the foregoing Table, particularly favorable for electrolytic surface graining are those having an aluminum purity of not less than 99.9% by weight, preferably not less than 99.5% by weight.
On the other hand, those having an aluminum content of less than 99.0% by weight show high strength, but are inferior in electrolytic surface graining properties.